Surprise! Facebook’s gotten in hot water for doing something creepy. Over the weekend it was revealed that Facebook secretly conducted a massive psychological experiment on some 600,000 of its users by trying to see if it could manipulate their mood by showing them mostly either happy posts or sad posts on their feeds.

The point of the experiment was to see whether being subjected to either happy news or sad news from friends would make Facebook users more likely to write happy posts or sad posts of their own, and sure enough, if you saw nothing but happy posts you were more likely to write something happy and vice versa.

It goes without saying that this has been a tad controversial, however. Slate’s Katy Waldman, for one, has decried the Facebook experiment as “unethical” in part because the company “intentionally made thousands upon thousands of people sad” and because this kind of research typically requires some kind of informed consent.

Facebook data scientist Adam Kramer, who was one of the authors of the study, has now written a post in which he defends the study’s goals but admits that the way the experiment was described in the research paper made it sound much worse than it actually was and sparked some legitimate worries from Facebook users about how they’re being manipulated by the company.

“Having written and designed this experiment myself, I can tell you that our goal was never to upset anyone,” he says. “I can understand why some people have concerns about it, and my coauthors and I are very sorry for the way the paper described the research and any anxiety it caused. In hindsight, the research benefits of the paper may not have justified all of this anxiety.”

Kramer also emphasizes that this study was conducted in “early 2012” and that Facebook has refined its internal review practices since then, which presumably means it won’t conduct mood manipulation experiments like this in the future.

That said, this really does open up some legitimate questions about what Facebook is actually doing with all our data. The mood manipulation experiment may only be the tip of the iceberg and we may never know what other ways the company is using us for psychological experiments behind the scenes without our knowledge.